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Mukul Sharma - One of the best experts on this subject based on the ideXlab platform.
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lithologic controls on Osmium Isotopes in the rio orinoco
Earth and Planetary Science Letters, 2006Co-Authors: Cynthia Chen, Mukul Sharma, Benjamin C BostickAbstract:Abstract The seawater 187Os/188Os ratio has been increasing over the last 50 Ma and at present is ∼ 1.06 reflecting that about 80% of Os in the oceans is derived from the continents that provide Os with an average 187Os/188Os ratio of about 1.26. Whether the past variations in seawater Os Isotopes record changes in the bulk Os flux with an average isotopic composition or the changes in the average 187Os/188Os ratio of the continental inputs or a combination of these two pathways is not clear. The fundamental importance of lithology in controlling continental weathering rates and dissolved ion yields has been well established for the major cations. It is dramatically manifested in the Sr Isotopes of rivers that are affected by selective dissolution of carbonates. Accordingly, for Os Isotopes it has been proposed that disproportionate contributions of Os with extremely high 187Os/188Os ratio come from weathering of organic-rich black shales. Here we examine the effect of the weathering of specific lithologies on Osmium isotopic composition and concentration in water samples of the Orinoco River basin, a major river basin draining both black shales exposed in the Northern Andes and granites of the Precambrian Guyana Shield. The Northern Andes was uplifted ~17 Ma, which corresponds to the time of a dramatic rise in 187Os/188Os ratio. The Osmium isotopic composition and concentrations vary considerably in the tributaries and the main stem of the Orinoco; the highest Os concentrations are observed in the rivers draining the Andes. However, waters draining the Andes are not highly radiogenic (187Os/188Os
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Osmium Isotopes in hydrothermal fluids from the juan de fuca ridge
Earth and Planetary Science Letters, 2000Co-Authors: Mukul Sharma, G J Wasserburg, Albrecht W Hofmann, David A ButterfieldAbstract:We present Os data for axial high-temperature and off-axial low-temperature hydrothermal solutions from the Juan de Fuca Ridge. The high-temperature, H₂S-bearing axial fluids have unradiogenic Os Isotopes pointing to a nearly complete domination of Osmium Isotopes from the basalts during hydrothermal circulation. The ridge axis fluids typically do not show large enrichment in Osmium concentration over seawater although one high-temperature fluid has an Os concentration enhanced by a factor of 4 above seawater. It appears that the Os concentration of high-temperature hydrothermal fluids is typically buffered at roughly the seawater concentration. We suggest that subseafloor precipitation of pyrite from the high-temperature hydrothermal fluids controls the Osmium transportation. The axial hydrothermal activity does not supply significant amounts of unradiogenic Osmium to the deep oceans. In contrast, a low-temperature off-axis fluid is enriched in non-radiogenic Osmium over seawater by a factor of 9, showing much less precipitation of Osmium at low temperature. Because a large fraction of the cooling of oceanic lithosphere occurs on ridge flanks, Os from low-temperature, ridge-flank hydrothermal circulation may be a significant contributor to the balance of Os in the oceans. A detailed balance between Os contributions from dissolution of cosmic dust and hydrothermal fluids is still not possible. The low-temperature hydrothermal sample gives ¹⁸⁷Os/¹⁸⁸Os = 0.110 ± 0.001. This extremely unradiogenic Osmium can only come from a source that underwent depletion of Re over 2.6 Ga ago. Assuming no contamination during sample collection, this result suggests that the convecting upper mantle contains ancient depleted material that imparted unradiogenic Osmium to intruding basaltic melts.
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Osmium Isotopes in hydrothermal uids from the juan de fuca ridge
2000Co-Authors: Mukul SharmaAbstract:We present Os data for axial high-temperature and off-axial low-temperature hydrothermal solutions from the Juan de Fuca Ridge. The high-temperature, H2S-bearing axial fluids have unradiogenic Os Isotopes pointing to a nearly complete domination of Osmium Isotopes from the basalts during hydrothermal circulation. The ridge axis fluids typically do not show large enrichment in Osmium concentration over seawater although one high-temperature fluid has an Os concentration enhanced by a factor of 4 above seawater. It appears that the Os concentration of hightemperature hydrothermal fluids is typically buffered at roughly the seawater concentration. We suggest that subseafloor precipitation of pyrite from the high-temperature hydrothermal fluids controls the Osmium transportation. The axial hydrothermal activity does not supply significant amounts of unradiogenic Osmium to the deep oceans. In contrast, a low-temperature off-axis fluid is enriched in non-radiogenic Osmium over seawater by a factor of 9, showing much less precipitation of Osmium at low temperature. Because a large fraction of the cooling of oceanic lithosphere occurs on ridge flanks, Os from low-temperature, ridge-flank hydrothermal circulation may be a significant contributor to the balance of Os in the oceans. A detailed balance between Os contributions from dissolution of cosmic dust and hydrothermal fluids is still not possible. The low-temperature hydrothermal sample gives 187 Os/ 188 Os = 0.110 ˛ 0.001. This extremely unradiogenic Osmium can only come from a source that underwent depletion of Re over 2.6 Ga ago. Assuming no contamination during sample collection, this result suggests that the convecting upper mantle contains ancient depleted material that imparted unradiogenic Osmium to intruding basaltic melts. fl 2000 Elsevier Science B.V. All rights reserved.
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himalayan uplift and Osmium Isotopes in oceans and rivers
Geochimica et Cosmochimica Acta, 1999Co-Authors: Mukul Sharma, G J Wasserburg, Albrecht W Hofmann, G J ChakrapaniAbstract:Previous studies have shown that ^(187)Os/^(188)Os in seawater has become increasingly radiogenic over the last 40 Ma in a manner analogous to strontium. This rapid rise in the marine ^(187)Os/^(188)Os over the last 17 Ma has been attributed to an increase in the bulk silicate weathering rates resulting from the rise of the Himalayas and/or selective weathering and erosion of highly radiogenic organic rich ancient sediments. The key test of this hypothesis is the ^(187)Os/^(188)Os and the total Osmium concentration of the Himalayan rivers. We report the concentration and isotopic composition of Osmium in the Ganges, the Brahmaputra, and the Indus rivers. The ^(187)Os/^(188)Os of the Ganges close to its source (at Kaudiyal, 30°05′N, 78°50′E) is 2.65 and [Os] = 45 fM/kg. A second sample of the lower reaches of the Ganges at Patna (25°30′N, 85°10′E) gives ^(187)Os/^(188)Os =1.59 and [Os] = 171 fM/kg. The ^(187)Os/^(188)Os of the Brahmaputra at Guwahati (26°10′N, 91°58′E) is 1.07 and [Os] = 52 fM/kg. A sample of the Indus (Besham, 34°55′N, 72°51′E) has a ^(187)Os/^(188)Os of 1.2 and [Os] = 59 fM/kg. We infer that the Himalayas do not provide either a high flow of Osmium or a highly radiogenic Osmium component to the oceans. The overall trend for Osmium and strontium could be explained by a regularly increasing input of global continental weathering sources but the Himalayas themselves appear not to be the dominant source.
T Alexander - One of the best experts on this subject based on the ideXlab platform.
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shape evolution in the neutron rich Osmium Isotopes prompt gamma ray spectroscopy of os 196
Physical Review C, 2014Co-Authors: P. R. John, V. Modamio, D. Mengoni, S. Lunardi, J J Valientedobon, Tomas R Rodriguez, D Bazzacco, A Gadea, C Wheldon, T AlexanderAbstract:The shape transition in the neutron-rich Os Isotopes is studied by investigating the neutron-rich Os-196 nucleus through in-beam gamma-ray spectroscopy using a two-proton transfer reaction from a Pt-198 target to a Se-82 beam. The beam-like recoils were detected and identified with the large-acceptance magnetic spectrometer PRISMA, and the coincident gamma rays were measured with the advanced gamma tracking array (AGATA) demonstrator. The de-excitation of the low-lying levels of the yrast-band of Os-196 were identified for the first time. The results are compared with state-of-the-art beyond-mean-field calculations, performed for the even-even Os188-198 Isotopes. The new results suggest a smooth transition in the Os Isotopes from a more axial rotational behavior towards predominately vibrational nuclei through triaxial configurations. An almost perfect gamma-unstable/triaxial rotor yrast band is predicted for Os-196 which is in agreement with the experimentally measured excited states.
P. R. John - One of the best experts on this subject based on the ideXlab platform.
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Shape Evolution in the Neutron-rich Osmium Isotopes: Prompt $\gamma $-ray Spectroscopy of ${}^{196}$Os
Acta Physica Polonica B, 2015Co-Authors: P. R. John, V. Modamio, J. J. Valiente-dobón, D. Mengoni, S. Lunardi, T.r. RodríguezAbstract:In order to investigate the shape evolution in the neutron-rich Osmium Isotopes, the first in-beam-ray spectroscopic measurement of 196Os was performed at the Laboratori Nazionali di Legnaro, Italy. 196Os was populated in the two-proton-transfer channel 198Pt(82Se, 84Kr)196Os with a beam energy of 426 MeV. The beam-like recoils were detected in the largeacceptance magnetic spectrometer PRISMA and the coincident rays were measured by the AGATA demonstrator. The de-excitation of the two lowest-lying yrast states was observed for the first time and a candidate for the 6+1-level was found. The comparison with state-of-the-art beyond mean-field calculations reveal the -soft character of 196Os
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shape evolution in the neutron rich Osmium Isotopes prompt gamma ray spectroscopy of os 196
Physical Review C, 2014Co-Authors: P. R. John, V. Modamio, D. Mengoni, S. Lunardi, J J Valientedobon, Tomas R Rodriguez, D Bazzacco, A Gadea, C Wheldon, T AlexanderAbstract:The shape transition in the neutron-rich Os Isotopes is studied by investigating the neutron-rich Os-196 nucleus through in-beam gamma-ray spectroscopy using a two-proton transfer reaction from a Pt-198 target to a Se-82 beam. The beam-like recoils were detected and identified with the large-acceptance magnetic spectrometer PRISMA, and the coincident gamma rays were measured with the advanced gamma tracking array (AGATA) demonstrator. The de-excitation of the low-lying levels of the yrast-band of Os-196 were identified for the first time. The results are compared with state-of-the-art beyond-mean-field calculations, performed for the even-even Os188-198 Isotopes. The new results suggest a smooth transition in the Os Isotopes from a more axial rotational behavior towards predominately vibrational nuclei through triaxial configurations. An almost perfect gamma-unstable/triaxial rotor yrast band is predicted for Os-196 which is in agreement with the experimentally measured excited states.
R F Casten - One of the best experts on this subject based on the ideXlab platform.
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multiple β decaying states in 194 re shape evolution in neutron rich Osmium Isotopes
Physical Review C, 2012Co-Authors: N Aldahan, G.d. Dracoulis., P H Regan, Zs Podolyak, P M Walker, N Alkhomashi, G F Farrelly, J Benlliure, S Pietri, R F CastenAbstract:beta decays from heavy, neutron-rich nuclei with A similar to 190 have been investigated following their production via the relativistic projectile fragmentation of an E/A = 1 GeV Pb-208 primary beam on a similar to 2.5 g/cm(2) Be-9 target. The reaction products were separated and identified using the GSI FRagment Separator (FRS) and stopped in the RISING active stopper. gamma decays were observed and correlated with these secondary ions on an event-by-event basis such that gamma-ray transitions following from both internal (isomeric) and beta decays were recorded. A number of discrete, beta-delayed gamma-ray transitions associated with beta decays from Re-194 to excited states in Os-194 have been observed, including previously reported decays from the yrast I-pi = (6(+)) state. Three previously unreported gamma-ray transitions with energies 194, 349, and 554 keV are also identified; these transitions are associated with decays from higher spin states in Os-194. The results of these investigations are compared with theoretical predictions from Nilsson multi-quasiparticle (MQP) calculations. Based on lifetime measurements and the observed feeding pattern to states in Os-194, it is concluded that there are three beta(-)-decaying states in Re-194. (Less)
S. Lunardi - One of the best experts on this subject based on the ideXlab platform.
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Shape Evolution in the Neutron-rich Osmium Isotopes: Prompt $\gamma $-ray Spectroscopy of ${}^{196}$Os
Acta Physica Polonica B, 2015Co-Authors: P. R. John, V. Modamio, J. J. Valiente-dobón, D. Mengoni, S. Lunardi, T.r. RodríguezAbstract:In order to investigate the shape evolution in the neutron-rich Osmium Isotopes, the first in-beam-ray spectroscopic measurement of 196Os was performed at the Laboratori Nazionali di Legnaro, Italy. 196Os was populated in the two-proton-transfer channel 198Pt(82Se, 84Kr)196Os with a beam energy of 426 MeV. The beam-like recoils were detected in the largeacceptance magnetic spectrometer PRISMA and the coincident rays were measured by the AGATA demonstrator. The de-excitation of the two lowest-lying yrast states was observed for the first time and a candidate for the 6+1-level was found. The comparison with state-of-the-art beyond mean-field calculations reveal the -soft character of 196Os
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shape evolution in the neutron rich Osmium Isotopes prompt gamma ray spectroscopy of os 196
Physical Review C, 2014Co-Authors: P. R. John, V. Modamio, D. Mengoni, S. Lunardi, J J Valientedobon, Tomas R Rodriguez, D Bazzacco, A Gadea, C Wheldon, T AlexanderAbstract:The shape transition in the neutron-rich Os Isotopes is studied by investigating the neutron-rich Os-196 nucleus through in-beam gamma-ray spectroscopy using a two-proton transfer reaction from a Pt-198 target to a Se-82 beam. The beam-like recoils were detected and identified with the large-acceptance magnetic spectrometer PRISMA, and the coincident gamma rays were measured with the advanced gamma tracking array (AGATA) demonstrator. The de-excitation of the low-lying levels of the yrast-band of Os-196 were identified for the first time. The results are compared with state-of-the-art beyond-mean-field calculations, performed for the even-even Os188-198 Isotopes. The new results suggest a smooth transition in the Os Isotopes from a more axial rotational behavior towards predominately vibrational nuclei through triaxial configurations. An almost perfect gamma-unstable/triaxial rotor yrast band is predicted for Os-196 which is in agreement with the experimentally measured excited states.